In the field of mass spectrometry, time-of-flight (TOF) techniques are well known. Typical of those techniques and principles of electron beam characteristics are discussed in the following articles and United States patent:
Pierce, J. R., Theory and Design of Electron Beams, 2nd Edition, Van Nostrand, New York (1954). PA0 Sanzone, G., Energy Resolution of the Conventional Time-of-Flight Mass Spectrometer, The Review of Scientific Instruments, Volume 41, Number 5, 741-2 (May, 1970). PA0 de Heer, W. A., P. Milani, Large Ion Volume Time-of-Flight Mass Spectrometer with Position- and Velocity-Sensitive Detection Capabilities for Cluster Beams, Rev. Sci. Instrum., Volume 62, No. 3, 670-7 (March, 1991). PA0 Sinha, M. P., G. Gutnikov, Development of a Miniaturized Gas Chromatograph-Mass Spectrometer with a Microbore Capillary Column and an Array Detector, Analytical Chemistry, Volume 63, Number 18, 2012-6 (September, 1991). PA0 Guilhaus, M., Spontaneous and Deflected Drift-Trajectories in Orthogonal Acceleration Time-of-Flight Mass Spectrometry, Journal of the American Society for Mass Spectrometry, Volume 5, 588-595 (1994). PA0 Meuzelaar, H. L. C., Man-Portable GC/MS, Opportunities, Challenges and Future Directions, Center for Micro Analysis & Reaction Chemistry, University of Utah. PA0 U.S. Pat. No. 5,117,107, entitled "Mass Spectrometer", issued to M. Guilhaus, et al., on May 26, 1992, for which Reexamination Certificate No. B1 5,117,107 was issued on Sep. 13, 1994.
Reflectron-type time-of-flight mass spectrometers are disclosed in U.S. Pat. Nos. 4,731,532 issued to R. Frey, et al., on Mar. 15, 1988; and 5,032,722 issued to U. Boesl, et al., on Jul. 16, 1991.
Time-of-flight mass spectrometers of the reflectron type incorporating an ion mirror have also been disclosed in U.S. Pat. No. 3,727,047, issued to Janes in April, 1973, and in German patent application No. 34 28 944. The ion mirror or reflector in these spectrometers is comprised of a series of grid electrodes to which voltages are applied to compensate for time differences in the total time of flight of the ions caused by different initial energies of the ions produced and subsequently accelerated out of the source region. This compensation results in improved mass resolution over the case of a linear (un-reflected) spectrometer. These gridded instruments suffer from loss of sensitivity due to ions being scattered or absorbed by the grids. Even if the grids are highly transmitting, significant losses will occur. For instance, reflection of an ion beam through five 80% transmitting grids will reduce instrument sensitivity by 90%.
The '532 patent referenced above discloses a gridless reflectron. However this instrument employs an entirely different voltage scheme from the present invention. The device disclosed in the '532 patent incorporates diaphragm rings in the two-stage ion mirror defining c.backslash.varied diameters. As a result, manufacture, assembly, and servicing of the instrument are complicated. Further, transmission of the ions is reduced, as well as mass resolution.
Accordingly, it is an object of the present invention to provide a reflectron-type time of flight mass spectrometer (TOF-MS) constructed in such a manner as to facilitate manufacture, assembly and servicing thereof
In light of this object, it is an object of the present invention to provide such a TOF-MS having a two-stage ion mirror having diaphragm rings each configured identical one to another in order to increase ion transmission and mass resolution.
It is a further object of the present invention to provide a TOF-MS having an ion mirror which is a two-stage mirror being second-order-corrected, energy-focusing and gridless.
Further, it is an object of the present invention to provide a TOF-MS having an ion source employing a near-ground voltage configuration.